1. Toss the squash and onion with 1/4 teaspoon salt and the pepper, then drizzle with olive oil. Divide between two baking sheets and bake in a preheated oven at 375 degrees for approximately 15-20 minutes or until soft. Stir occasionally.

2. Remove the baking sheets from the oven, sprinkle the slivered garlic on top, toss, then bake another 15 minutes. Remove from the oven and set aside.

3. In a separate pan, melt the butter and flour over medium heat, stirring constantly to create a thick paste. Cook for approximately 2 minutes.

4. Whisk in the cream and mix well, cooking for another 2-3 minutes before stirring in the lemon zest and the remaining salt. Remove the pan from heat.

5. Carefully add the roasted vegetables and cooked pasta to a large serving dish, pouring the cream sauce on top. Spread the basil over everything and toss well to combine.